The present invention relates to methods of processing workpieces having a multiplicity of recesses formed in an exposed surface and in particular, but not exclusively, where those recesses are of high aspect ratio and are present in high density.
In both the fields of micro engineering and the formation of semiconductor devices, it is becoming increasingly necessary to be able to fill recesses having high aspect ratios, particularly in order to form conductive paths between parts of the devices. In the field of semiconductor devices in particular, there is an increasing need to be able to fill such recesses when they are arrayed very close together and/or in high densities.
In our European Patent Application No. 0 516 344, we describe a method of filling such recesses which comprises the steps of depositing a layer of material on to the exposed surface of a workpiece having a multiplicity of recesses until all the recesses are bridged and then applying elevated temperatures and pressures to the layer so that the layer is deformed, without melting, to fill the respective recesses. In general, this process has been extremely successful in dealing with the problem of high aspect ratio recesses, but difficulties have been experienced, when there is a high density of recesses or when the grain structure of the deposited layer is such that localised shearing takes places as the material moves down into the recess.
From one aspect the invention consists in a method of processing a workpiece having a multiplicity of recesses formed in an exposed surface, the material comprising depositing a first layer of material on the exposed surface over all the recesses to close the openings, depositing a second layer on top of the first and applying heat and pressure to the layers such that the first layer is urged into the recesses to fill them.
From another aspect the present invention consists in a method of processing a workpiece having a multiplicity of recesses formed in an exposed surface, the method comprising depositing a first layer of material on the exposed surface until the first layer extends over all the recesses to close completely the openings of all the recesses in the exposed surface and subjecting the wafer and the first layer to elevated pressure and an elevated temperature sufficient to cause parts of the first layer to deform, without melting, to fill respective recesses characterised in that a second layer of material is deposited on the top of the first layer prior to or during the application of temperature and pressure.
It is particularly preferred that the second layer is an anti-reflective coating, because such a coating is required at a later stage in the normal production sequence. This layer may be deposited by sputtering or other suitable technique and may for example be titanium nitride.
Where the first layer is a metal, the second layer may be an oxide or nitride of the first layer. For example, a native oxide may be formed by introducing oxygen or exposing the wafer to atmosphere by means of a xe2x80x9cvacuum breakxe2x80x9d. The nitride may be formed by exposing the second layer to nitrogen during the application of high pressure.
The second layer is thin relative to the first layer. For example, if it is an oxide, the layer may be in the range of 15 xc3x85 to 25 xc3x85 or an anti-reflective coating may be typically be of the order of 100 xc3x85 to 500 xc3x85. This contrasts with the first layer of thickness, which, for aluminium alloy, may be typically be 2500 xc3x85 to 50,000 xc3x85. Usually the first layer will be a metallic electrical conductor such as an aluminium alloy, copper or gold. Gold would require a coating such as titanium nitride as it does not readily form oxides or nitrides.
The method may also include depositing a thin layer of material prior to the deposition of the first layer to form a barrier or lubricating layer. This may be titanium nitride or indeed a prior layer of the material of the first layer.
The invention also includes devices formed using such a process.
Although the invention has been defined above it is to be understood that it covers any inventive combination of the features set out above or in the following description.